Examples of a technology regarding a spectroscopic measurement device using terahertz waves include a spectroscopic measurement device described in Japanese Patent No. 5231538. In this spectroscopic measurement device, a terahertz wave generation element that generates terahertz waves is integrally provided on an incidence surface of an internal total reflection prism, and a terahertz wave detection element that detects the terahertz waves is integrally provided on an emission surface of the internal total reflection prism. In this total reflection terahertz measurement device, the terahertz waves are totally reflected by a placement surface for a measurement target provided in the internal total reflection prism so that an evanescent component is generated, and the measurement target is irradiated with the evanescent component so that information on the measurement target is acquired.
Examples of a technology regarding a method of detecting terahertz waves include detection methods described in Non-Patent Document 1 and Non-Patent Document 2. In these detection methods, terahertz waves and probe light having a wavelength different from that of the terahertz waves are incident on a nonlinear crystal, wavelength conversion is performed, and the terahertz waves are indirectly detected on the basis of wavelength converted light. Examples of a light source that simultaneously outputs terahertz waves and probe light include a quantum cascade laser described in Japanese Unexamined Patent Publication No. 2017-33981. This quantum cascade laser is configured to be able to generate first pump light at a first frequency and second pump light at a second frequency due to a light emission transition between sub-bands of electrons, and to generate output light of the terahertz waves at a difference frequency due to difference frequency generation using the first pump light and the second pump light.    [Non-Patent Document 1] Yuma Takida et al., “Nonlinear optical detection of terahertz-wave radiation from resistant tunneling diodes,” Optics Express 255, 5389 (2017).    [Non-Patent Document 2] Vladimir V. Komienko et al., “Terahertz continuous wave nonlinear-optical detection without phase-locking between a source and detector,” Optics Letters 41, 4075 (2016).